Search Results (384)

The stabilization of soft, organic-rich soils with cement is often hindered by retarded hydration and poor long-term performance under cyclic loads. While nano-silica or sand are known modifiers, their individual efficacy in high-organic environments remains limited, and a systematic comparison of their composite effect across different soil types is lacking. This study investigates the synergistic enhancement of cement-stabilized soils using a combined nano-SiO₂ and sand composite, comparing its effectiveness in high-organic soft soil and low-organic clay. Laboratory tests, including unconfined compressive strength (UCS), cyclic loading, scanning electron microscopy (SEM), and X-ray diffraction (XRD), were conducted. Results showed a stark contrast in 28-day UCS between unmodified soft soil cement (0.13 MPa) and clay cement (1.04 MPa). The optimal composite of 3.5% nano-SiO₂ and 40% sand increased the 28-day UCS to 1.39 MPa for soft soil (a 969% improvement) and 5.51 MPa for clay (a 430% improvement), respectively. Notably, under a cyclic stress ratio (CSR) of 0.7~0.8, unmodified specimens failed after fewer than 120 load cycles, whereas the composite-modified soils withstood 20,000 cycles without failure, demonstrating exceptional fatigue resistance independent of static strength gain. Microstructural analysis revealed that the composite effectively promoted the formation of cementitious hydration products, counteracting the inhibitory effect of organic matter. This research demonstrates that the nano-silica sand composite provides a superior and more broadly applicable improvement for cement-stabilized soils across the tested organic content range (3.3–7.7% LOI) compared to single-additive approaches, significantly enhancing both mechanical strength and long-term durability. Full article

Efficient recovery of ammonia from sludge hydrolysate (SH) remains a challenging task. This study developed a superhydrophobic capillary ceramic-membrane contactors (MCs), which, by establishing a stable gas-phase mass transfer interface, provides a reliable guarantee for ammonia recovery under high-temperature, high-pH, and high-organic-load conditions. In a controllable simulation system, the system investigated the effects of key operational parameters such as pH, flow rate, and feed ammonia concentration on ammonia mass transfer behavior, and verified the feasibility of this MCs in efficient ammonia removal. Then, this membrane contactor was applied to the actual sludge hydrolysate (SH) system, and its anti-pollution effects, wetting stability, and adaptability to fluctuating conditions under long-term continuous operation were evaluated. The results showed that after operating for 10 h, the ammonia removal in the simulation system and the actual system reached 93.6% and 90.3%, respectively. During long-term operation, the ammonia recovery reached 90.3%. Meanwhile, the organic matter in SH was completely retained, and (NH₄)₂SO₄ was not contaminated by organic matter. Throughout the entire operation process, the contact angle of the membrane remained above 129.6°. This study provides a theoretical basis and practical reference for recovering ammonia using a hydrophobic capillary ceramic-membrane contactor in SH. Full article

Agricultural drainage water is a significant contributor to a broad spectrum of pollutant loads, including nitrates, ammonium, organic matter, phosphorus, and emerging substances, and thus poses an important environmental and human health concern. This review aims to integrate existing knowledge on bioreactors and natural and constructed wetlands in the treatment of agricultural drainage water. It covers bioreactors from a perspective on categorization, principles, and performance with respect to treatment efficiency. It provides a critical evaluation of constructed wetlands as passive treatment systems, in addition to their importance as nature-based service providers. Some significant issues in bioreactors, such as media durability, greenhouse gas production, and the elimination of emerging pollutants, will be critically described, and this critique will conclude with proposals for possible path methods in bioreactors toward a suitable convergence with a nature-related water treatment system. Full article

The wastewater generated during coffee processing contains high levels of acidity and organic matter, posing substantial environmental hazards, particularly in rural areas where traditional treatment methods are financially infeasible. This research assesses the field-scale effectiveness of Chrysopogon zizanioides (vetiver grass) in phytoremediation of coffee wastewater in Huánuco, Peru, with particular attention to how plant maturity affects treatment outcomes. A comparative analysis was performed on untreated and vetiver-filtered effluent from infiltration ponds at four growth stages (6, 8, 19, and 21 months), with measurements of pH, chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), and suspended solids (TSS, SS) conducted according to standardized methods. The findings indicate notable improvements in water quality, as the pH rose from 4.07 ± 0.32 to 5.82 ± 0.40 (p < 0.001) and organic loads decreased by 39–41% (COD: 38,600 ± 12,100 to 23,000 ± 8500 mg L⁻¹ O₂; BOD₅: 27,700 ± 9400 to 16,500 ± 5600 mg L⁻¹ O₂). Total Suspended Solids (TSS) were reduced by 26%, while the settleable suspended solids fraction (SS) decreased by 69%, indicating strong particulate removal through combined filtration and sedimentation mechanisms. Mature vetiver stands (21 months old) showed better results, underscoring the importance of root development for effective phytoremediation. Strong correlations were observed between COD and BOD₅ (r = 0.92), while pH negatively correlated with organic and particulate parameters. The study presents empirical evidence supporting vetiver-based systems as an economical and sustainable approach to decentralized wastewater treatment in coffee-growing areas. Furthermore, it provides actionable insights for improving phytoremediation by focusing on plant maturity, which can be readily adapted for large-scale implementation in resource-constrained settings. The findings underscore the potential of nature-based technologies to address environmental challenges while supporting local economies dependent on coffee production. Full article

Loading dissolved organic matter (DOM) onto iron–manganese oxides (FeMnOx) was a promising strategy for enhancing the hexavalent chromium (Cr(VI)) removal from wastewater. To optimize this process and gain deeper mechanistic insight, this study systematically investigated the DOM loading characteristics onto FeMnOx and its subsequent effect on Cr(VI) adsorption. DOM loading onto FeMnOx was significantly affected by the initial concentration of DOM and pH, with optimal loading conditions identified as a DOM concentration of 75 mg/L, pH of 4, ionic strength of 0.005 mol/L, temperature of 50 °C, and contact time of 4 h. During loading, FeMnOx preferentially adsorbed low-molecular-weight/low-aromaticity components such as tryptophan-like (C1) and fulvic acid-like (C2) substances. The adsorption process followed a non-uniform monolayer surface adsorption and involved multiple stages dominated by chemical interactions. DOM coating on FeMnOx significantly enhanced the Cr(VI) removal, and the maximum adsorption capacity under optimal loading conditions increased from 18.46 mg/g to 23.26 mg/g. Characterization by SEM-EDS, BET, ICP-MS, XPS, FTIR, and CV revealed that a moderate DOM loading (55–75 mg/L) enhanced the material’s surface reducibility and mesoporous structure. This improvement was attributed to the reduction of surface Mn(IV) to more-reactive Mn(III) by reductive functional groups in DOM, thereby promoting Cr(VI) adsorption and reduction. In contrast, excessive DOM loading (105 mg/L) formed a dense organic layer that masked active sites and hindered electron transfer, ultimately compromising the long-term reductive capability. These findings elucidate the concentration-dependent regulatory role of DOM in modifying FeMnOx properties, providing a theoretical foundation for the rational design of efficient DOM–metal oxide composites for heavy metal remediation in aquatic environments. Full article

Thermal hydrolysis pretreatment (THP) increases the solubilization of sewage sludge, while bioelectrochemically assisted anaerobic digestion (BEAD) enhances the conversion of the solubilized organic matter into methane and improves reactor stability in the presence of inhibitory compounds. In this study, by mapping methane production in a BEAD reactor against the soluble organic loading rate (sOLR), determined from soluble chemical oxygen demand (sCOD) measurements, distinct operational regimes corresponding to different THP temperatures were identified. With the 120 °C pretreated feedstock, the BEAD reactor operated in a hydrolysis-limited regime, where increasing sOLR increased methane production but reduced conversion efficiency. Accordingly, at an sOLR of 4.5 g (L_R d)⁻¹, a volumetric methane production rate of 0.8 L L_R⁻¹ was achieved. Increasing THP severity to 150 °C improved solids solubilization and shifted the system into a kinetically enhanced regime, in which methane production was directly proportional to sOLR, indicating improved substrate accessibility and reaction kinetics. Consequently, at an sOLR of 7.75 g (L_R d)⁻¹, methane production reached 1.46 L L_R⁻¹. This regime-based analysis provides quantitative guidance for selecting pretreatment severity and loading strategies to maximize methane production, while maintaining stable BEAD reactor operation at high organic loads. Full article

The persistence of water-soluble polymers such as polyvinylpyrrolidone (PVP) in aquatic environments presents a major challenge for conventional wastewater treatment. Herein, a sunlight-active TiO₂/activated carbon (TiO₂/AC) composite fabricated via a simple physical mixing route is reported for the synergistic adsorption and photocatalytic mineralization of PVP K30. The optimal composite (2:1 weight ratio) exhibits a high surface area (412 m² g⁻¹) and an integrated anatase–carbon architecture. The process operates through a sequential “adsorb-and-shuttle” mechanism, whereby PVP is first concentrated on the composite in the dark (30.2% removal in 8 h) and subsequently degraded under solar irradiation. This dual function leads to 86.4% PVP removal and 72.1% total organic carbon (TOC) mineralization, demonstrating true polymer destruction rather than mere surface accumulation. The composite demonstrates robust performance in simulated wastewater, retaining over 68% PVP removal and 55% TOC mineralization in a complex matrix containing competing inorganic ions and natural organic matter. Spectroscopic and thermogravimetric analyses confirm PVP chain scission and near-complete removal of adsorbed residues. An optimized ethanol-washing protocol enables effective catalyst regeneration, with the composite retaining 85% of its initial activity after five cycles. A detailed techno-economic analysis confirms the economic viability of this regeneration strategy at industrial scales (>1000 kg/year), projecting cost savings exceeding 60% compared to fresh catalyst use. Importantly, the PVP-loaded spent TiO₂–AC was successfully repurposed as an electrocatalyst for the urea oxidation reaction, achieving a high current density of 163.7 mA cm⁻², which surpasses the performance of the pristine composite. The greenness of the overall process was validated using analytical eco-scale (ESA), method volume intensity (AMVI), and white analytical chemistry (WAC) metrics. Overall, this work presents a sustainable, solar-driven platform that advances a circular economy model, integrating effective polymer wastewater remediation with subsequent energy valorization of the spent material. Full article

Maize silage can play a key role in policies aimed at stabilising local energy systems, as it constitutes a critical renewable feedstock for European biogas plants. By providing a dense and predictable source of chemical energy, it supports balance and reliability in the agricultural energy sector. To convert this potential into stable energy production, operators require kinetic models that translate routine silage quality indicators into concrete guidance for digester operation and control. Therefore, the aim of this article was to evaluate the batch kinetics of anaerobic digestion (AD) of maize silage and to select an adequate model for describing biochemical methane potential (BMP) profiles and associated energy recovery in the context of start-up, organic loading rate (OLR), hydraulic retention time (HRT) and feedstock preparation. Ten batches of silage (A–J) were examined, covering a realistic range of pH, electrical conductivity (EC), dry and volatile solids, ash, protein–fat–fibre fractions, fibre composition (NDF, ADF and ADL), derived fractions (hemicellulose, cellulose, and residual organic matter (OM)), C/N ratio and macro-/micronutrient profiles, including trace elements relevant to methanogenesis (Ni, Co, Mo, and Se). BMP tests were carried out in batch mode, and the resulting curves were fitted using the modified Gompertz and a first-order kinetic model. Methane yields of approx. 100–120 m³ CH₄/Mg fresh matter (FM) and 336–402 m³ CH₄/Mg volatile solids (VS), with CH₄ contents of 52–57% v/v, were typical for energy-grade maize silage. Kinetic and energetic behaviours were governed mainly by residual OM and hemicellulose (shortening the lag phase and increasing the maximum methane production rate), the ADL/cellulose ratio (controlling the slower hydrolytic tail), EC and Na/Cl/S (extending the lag phase), and C/N together with Ni/Co/Mo/Se (stabilising methanogenesis). The modified Gompertz model reproduced BMP curves with a pronounced lag phase and asymmetry more accurately (lower error and better information criterion values), and its parameters directly support start-up design, OLR ramp-up and energetic performance optimisation in bioenergy reactors. The novelty of this work lies in combining batch BMP tests, comparative kinetic modelling and detailed silage characterisation to establish quantitative links between kinetic parameters and routine maize silage quality indicators that are directly relevant for biogas plant operation and renewable energy production. Full article

This study evaluates the efficiency of several urban wastewater treatment configurations in reducing suspended solids (TSSs) and organic pollutants (BOD₅ and COD) under Montenegrin conditions. The systems tested include combinations of primary treatment and vertical-flow constructed wetlands (VFCWs) in three different configurations (VFCW1–VFCW3), with and without the addition of low doses of effective microorganisms (EMs). The results show that the inclusion of EMs significantly improves pollutant removal efficiency and system stability. Suspended solid removal reached over 90%, while organic matter removal was also high. Among the evaluated systems, those integrating microorganisms and optimized substrates required the smallest land area to achieve high treatment performance, with some configurations reducing land demand by over 70% compared to traditional systems. Under Montenegrin climatic conditions, the smallest required wetland area to achieve 95% BOD₅ removal was only 1.07 m²/PE in the PT-EM-VFCW3 system (primary treatment + effective microorganisms + vertical-flow constructed wetland configuration 3), which is comparable to or even more favorable than the best values reported in the literature. These findings suggest that enhanced wetland systems offer a sustainable and space-efficient solution for municipal wastewater treatment in areas with land constraints, such as Montenegro. Beyond treatment performance, the results highlight land-use reduction as the dominant economic benefit of the proposed configurations, while the integration of effective microorganisms provides additional operational flexibility under seasonal and variable loading conditions. Full article

Wine processing industries require a substantial amount of water and generate considerable volumes of wastewater. Winery wastewater (WWW) is notable for its high concentrations of biodegradable organic matter, while containing relatively low levels of nutrients. Due to seasonal variability in wastewater generation, treatment processes must be both efficient and adaptable. A range of wastewater treatment technologies are currently implemented at pilot and full scales, and ongoing research continues to yield innovative solutions in laboratory settings. This paper provides a comprehensive review of advancements in WWW treatment technologies, pinpoints gaps, and highlights future research directions. The treatment methods discussed include aerobic reactors, anaerobic systems, constructed wetlands (CWs) and biosand filters (BSFs), as well as advanced oxidation processes (AOPs). The advantages and limitations of these techniques, along with key factors affecting their performance, are examined. CWs are regarded as cost-effective and efficient solutions for small to medium wineries, whereas activated sludge and anaerobic digestion processes, which require a smaller footprint, are suitable for managing higher loads at large wineries. While anaerobic processes offer reduced operating costs, they often produce effluents of lower quality compared to aerobic processes, necessitating subsequent polishing prior to discharge. Advances in AOPs present promising alternatives for pre/post-treatment, facilitating the breakdown of persistent organics and achieving acceptable chemical oxygen demand (COD) levels. Nevertheless, further research is required to address operational optimization and reduce associated costs. Full article

This study evaluated the feasibility of using effluent from the anodic chamber of a microbial fuel cell (MFC), powered by real fruit and vegetable wastewater, as a cultivation medium for Tetraselmis subcordiformis, a microalga capable of bio-photolytic hydrogen production. In three experimental variants, different organic loading rates were applied in the anodic chamber, resulting in significant differences in effluent quality and its suitability as a culture medium. In contrast to the dominant MFC configurations, in which microalgae act as cathodic biocatalysts, the microbial fuel cell in this study was used as a source of the inevitable anode effluent, which was subsequently valorized as a cultivation medium for the marine microalga T. subcordiformis to support biomass and hydrogen production. In variants with moderate COD concentration and low lipid content, the highest biomass concentrations, ranging from 941 ± 104 mg VS/L to 1020 ± 108 mg VS/L, were obtained, along with the highest nitrogen assimilation efficiency (48.7–49.1%) and phosphorus assimilation efficiency (62.3–63.1%). The variant in which the culture medium contained the highest concentrations of COD, TSS, and lipids showed a substantial limitation of biomass growth to 745 ± 75 mg VS/L and lower nutrient removal efficiency (total nitrogen—42.3 ± 4.7%, total phosphorus—55.0 ± 5.0%). The obtained biomass was then used for H₂ production in a mineral photobiolytic medium. The highest total hydrogen production reached 184.7 ± 25.0 mL, while the specific hydrogen yield reached 193.7 ± 32.6 mL/g VS. Increased concentration of organic matter in the medium reduced total hydrogen production to 112.0 ± 14.8 mL, mainly due to lower biomass concentration, although the specific hydrogen yield remained high (153.4 ± 25.8 mL/g VS). The biogas composition was stable (H₂ 58.0–58.7%, CO₂ 35.3–35.9%, O₂ 6.0–6.2%). Full article

In South Asia, smog has become a critical environmental concern that endangers public health, ecosystems, and the regional climate. To determine the primary causes of smog formation in Lahore during peak polluted months (October and November), the current study develops a dual analytical framework that combines cutting-edge machine learning with sector- and pollutant-specific emission analysis. To assess their relationship with Air Quality Index (AQI) and create a high-accuracy predictive model, meteorological factors and emission data from key sectors are used to build Random Forest and extreme gradient boosting (XGBoost) models. The current study evaluates the joint effects of weather and emission loads on AQI variability by integrating atmospheric dynamics with comprehensive emission profiles. The XGBoost model forecasts important pollutants from the transportation, industrial, and agricultural sectors, including carbon dioxide (CO₂), oxides of nitrogen (NO_x), Volatile Organic Compounds (VOCs), and particulate matter, in the second analytical tier. Particulate matter (PM), NO_x, and transport-related pollutants are consistently identified by the models as the primary predictors of AQI, with high prediction performance. Furthermore, a 3-fold split is used for cross-validation, making sure that each fold maintained the data’s chronological order to avoid leakage. The model has modest root mean square error (RMSE) levels (4.32 and 8.14) and high coefficient of determination (R²) values (0.93–0.99). Approximately 90% of Lahore’s annual emissions resulted from the transportation sector. These results offer aid to policymakers to anticipate air quality, identify important emission sources, and execute targeted initiatives to minimize smog and promote a healthier urban environment. The current study also helps in analyzing the causes of atmospheric and sectoral pollution. While the study captures smog dynamics during peak pollution months, its temporal scope is limited, and finer spatial measurements could further improve the generalizability of the results. Full article

Meat-processing wastewater (MPWW) is rich in nutrients and organic matter. This study assessed its potential as feedstock for microalgal biomass production while enabling wastewater treatment. In batch assays, the microalgae-based consortium grew in raw MPWW, and its synergy with the native wastewater microbial community enhanced the chemical oxygen demand (COD) removal rate. If suspended solids were pre-removed from wastewater, COD removing rates improved from 828.5 ± 60.5 to 1097.5 ± 22.2 mg L⁻¹ d⁻¹. In a raceway system operated in fed-batch mode with sieved and sedimented MPWW, COD removal was consistently achieved across feeding cycles, despite the variability in wastewater composition, reaching rates of up to 806.3 ± 0.0 mg L⁻¹ d⁻¹. Total nitrogen also decreased in most cycles. Microalgal biomass, estimated from total photosynthetic pigment’s concentration, increased from 0.4 to 17.9 µg mL⁻¹. The microalgae-based consortium became more diverse over time, harboring at the end, additional eukaryotic taxa such as protozoan grazers and fungi (e.g., Heterolobosea class and Trichosporonaceae and Dipodascaceae families), although their roles in removal processes remain unknown. This study highlights the potential use of real MPWW as feedstock for microalgal-based biomass production with concomitant carbon/nutrient load reduction, aligning its implementation with circular economy percepts. Full article

This study addresses the issue of missing basic data and insufficient accuracy in predicting runoff and non-point-source pollution in the Heilongjiang region of China using the Soil and Water Assessment Tool (SWAT) model. Based on the China Ground Climate Data Daily Dataset (V3.0) and SPAW soil characteristic calculation formula, and assisted by the Python V3.0 language for data processing and computation, new high-precision weather generators and soil attribute databases suitable for the Heilongjiang region of China were established. The weather generator is based on daily data and contains detailed meteorological parameters such as temperature, humidity, wind speed, rainfall, etc., used to characterize the periodic changes in meteorological elements. And the differences and fluctuations outside this change curve were also retained in the basic construction of the weather generator. The soil database covers various parameters, such as soil type, texture, structure, nutrient content, organic matter content, etc., enabling the SWAT model to better simulate hydrological and pollutant transport processes in the soil. Additionally, point-source input data, including various industrial and domestic wastewater discharge situations, were collected and organized to improve data quality. Furthermore, a series of agricultural management measures were developed based on the use of fertilizers and pesticides for simulation, providing an important basis for analyzing non-point-source pollution using the SWAT model. By comparing the different results of the simulation using optimized databases, it is shown that the above work improved the simulation accuracy of the SWAT model in predicting runoff and pollution load in Heilongjiang, China. The NSE of runoff simulation increased from 0.923 to 0.988, and the NSE of ammonia nitrogen and CBOD simulation increased from 0.852 and 0.758 to 0.930 and 0.902, respectively. It is expected that these efforts will provide strong data support for subsequent research and provide a theoretical basis for government decision-makers to build scientifically rigorous and effective pollution control strategies. Full article

The meat industry generates wastewater with high organic matter loads, posing a significant environmental risk if not properly treated. The present study evaluated the performance of a horizontal subsurface flow constructed wetland (HSSF-CW) treating slaughterhouse effluents characterized by high-strength influent concentrations of 3570.51 ± 153.82 mg/L COD, 2114.33 ± 104.58 mg/L BOD₅, and 1173.77 ± 96.95 mg/L TOC. Furthermore, Response Surface Methodology (RSM) was employed to model and optimize the operational parameters. The independent variables considered were hydraulic retention time (HRT: 3, 5, and 10 days) and vegetation type (Heliconia latispatha, Typha latifolia, and polyculture). The results demonstrated a statistically significant improvement in treatment efficiency, achieving maximum removal efficiencies of 86.5% for COD, 89.4% for BOD₅, and 91.5% for TOC. The statistical models exhibited high accuracy (R² ≥ 0.996, p < 0.001). Adjusted response surface equations identified the polyculture with a 5-day HRT as the most favorable operational scenario. These findings confirm that properly designed and operated constructed wetlands represent a viable and sustainable alternative for treating high-load agro-industrial effluents, contributing to the protection of receiving water bodies. Future research should focus on full-scale studies and the inclusion of critical parameters such as nutrients and pathogens for a more comprehensive system characterization. Full article